Diesel injector nozzles are usually cylindrically shaped and typically include a gallery cavity, a larger-diameter central air hole intersecting the gallery cavity at a central location, and three spaced-apart smaller-diameter fuel holes intersecting the gallery cavity at spaced apart locations which are separate from the central location. Diesel injector nozzles also include spray holes in fluid communication with the gallery cavity. Diesel injector nozzles are used in diesel engines, such as, but not limited to, large diesel engines which power locomotives. In operation, fuel is injected through the fuel holes to the gallery cavity, and pressurized air is injected through the air hole to the gallery cavity. The air and the fuel become mixed in the gallery cavity and the fuel-air mixture then exits the nozzle through the spray holes into a combustion chamber, as is well known to those skilled in the art.
During the manufacture of a diesel injector nozzle, typically the spray holes are drilled after the air holes, the fuel holes, and the gallery cavity have been created. In mechanically drilling the fuel holes in the diesel injector nozzle workpiece, burrs sometimes form at the intersection of the fuel holes with the gallery cavity. A known electrochemical deburring (ECD) technique for removing such burrs inserts an electrically-insulative sleeve into the air hole and then inserts a tool electrode through the open center of the sleeve such that the tip of the tool electrode is positioned in the gallery cavity and such that an annularly-cylindrical channel is defined between the tool electrode and the sleeve. Alternatively, the channel can be created in the tool electrode itself or in the sleeve itself. An electrolyte flow is directed through the channel to the gallery cavity and then through the fuel holes from the gallery cavity. A direct-current voltage potential is then applied between the tip of the tool electrode and the diesel injector nozzle workpiece. The effect is to remove metal, including the burrs, in the general vicinity between the tool electrode and the intersections of the fuel holes with the gallery cavity. A typical gap between the tool electrode and the intersections of the fuel holes with the gallery cavity in a large diesel injector nozzle is more than three millimeters.
With such a large gap between the tool and the burrs, the ECD process has to proceed under a low current density (as per Ohm's law and Faraday's law of electrolysis) which leads to a low metal removal rate. The large gap causes surface defects in the workpiece due to selective metal dissolution, surface pitting, and unwanted metal removal outside the immediate deburring area.
What is needed is a more efficient method, and improved apparatus for carrying out such a method, for electrochemically deburring diesel injector nozzle workpieces.